Enhanced Denitrification Bioreactors Hold Promise for Mid-Atlantic Ditch Drainage

There is strong interest in adapting denitrifying bioreactors to mid-Atlantic drainage systems to help address Chesapeake Bay water quality goals. Three ditch drainage-oriented bioreactors were constructed in 2015 in Maryland to evaluate site-specific design and installation concerns and nitrate (NO3-N) removal. All three bioreactor types removed NO3-N, as measured by load and/or concentration reduction, showing promise for denitrifying bioreactors in the mid-Atlantic's low gradient Coastal Plain landscape. The ditch diversion bioreactor (25% NO3-N load reduction; 0.97 g NO3-N removed m(-3) d(-1)) and the sawdust denitrification wall adjacent to a ditch (> 90% NO3-N concentration reduction; 1.9-2.9 g NO3-N removed m(-3) d(-1)) had removal rates within range of the literature. The in-ditch bioreactor averaged 65% NO3-N concentration reduction, but sedimentation is expected to be one of the biggest challenges. A robust water balance is critical for future assessment of bioreactors' contribution to water quality improvement in low gradient mid-Atlantic landscapes.